Lightguides are waveguides that are typically used for guiding light emitted by light sources in various lighting solutions. The lightguides can be used for display lighting (e.g. back-lighting, front-lighting), keypad, keyboard and/or button lighting, interior lighting, and exterior lighting, among other applications. Conventional lightguides that are considered as thin may have a thickness of about 0.8 to about 1.0 mm and include micro-optical structures for incoupling light thereto and/or outcoupling light therefrom.
FIG. 1 illustrates a side view of an embodiment of a planar lightguide 102 including a plurality of micro-optical structures 106 implemented as surface relief forms on one side of the lightguide 102 for outcoupling 108 light emitted either by a light source 104a or an alternative light source 104b and transported in the lightguide 102 by total reflection. In the example of FIG. 1, light is outcoupled from the lightguide 102 via a top surface opposite to the bottom surface, the latter including the illustrated micro-optical structures 106. The lightguide may include optically transparent polymeric material, such as PMMA (polymethyl methacrylate), for example. The lightguides are often application-specific such that a desired illumination pattern can be precisely obtained. The light source such as a LED (light-emitting diode) may be incoupled via different parts of a lightguide; entity 104a represents an example of a border area/surface or edge-connected light source whereas entity 104b is an instance of top/bottom surface incoupling.
Lightguides may be manufactured according to a number of different processes. Lightguide layer production can be completed by means of continuous roll replication, or “roll-to-roll” replication, among other options. By applying this manufacturing method bulk material, such as optically transparent plastic film, may be utilized in surface relief replication. Different roll-to-roll methods are prior known and feasible for manufacturing micro-optic surface relief forms (e.g. structures), either refractive or diffractive, for many different applications. Several roll-to-roll methods are available, such as the ones by Reflexite, Avery Dennison, 3M, Epigem, Rolltronics, Polymicro, Printo project, among others. Other suitable production methods may include continuous or discrete casting methods (UV or thermal curing), compression molding, injection molding, continuous or discrete embossing, such as hard embossing, soft embossing and UV embossing, among others. Melt film can also be used.
Now referring to FIG. 2, a surface view of a planar, elongated lightguide 202 is shown with a substantially point-like source of light 204 configured such that the light emitted therefrom is incoupled to the lightguide 202 via a border surface thereof. A line 206 with an arrow indicating the major direction of propagating light has been depicted to illustrate inclusion of an incoupling structure for controlling the incoupling between the light source 204 and the lightguide 202.
FIG. 3a illustrates one example of a lightguide 302 including an incoupling structure 306 consisting of a number of surface relief forms, such as a grating structure, located directly at one end surface of the lightguide 302 in front of the LED 304.
FIG. 3b illustrates an example of a lightguide 302 including a separate incoupling structure 306 between the lightguide 302 and the LED 304.
Notwithstanding the above and various other existing solutions for incoupling light into a lightguide or some other target area few drawbacks have remained therein concerning the characteristics of the coupled light. Either the arrangements have been rather bulky and thus unsuitable for micro-scale applications wherein size restrictions for positioning the lightguide, light source and associated elements are considerable, or the results have functionally turned out only partially fulfilling due to unacceptably irregular illumination pattern obtained on a predetermined outcoupling surface, or to weak incoupling efficiency, for example.